[Design discussion] Editor implementation for Collaboration

Owned by Kartheek Palla
Feb 04, 2019

Overview:

This page explains the design of collaboration implementation inside Editor using lock and unlock a resource using lock service.

Design Wiki: Lock Service (https://project-sunbird.atlassian.net/wiki/spaces/SBDES/pages/create?useDraft=true&draftId=715292797&draftShareId=4c68f0ea-0cdc-4886-aecb-dd1bb70c6aed)

Currently in editors only content creator can edit his contents that he created. if he wants to ask some other user(teacher/colleague) to request to just cross check it for improvement, user needs to share his credentials.

Problem Statement

Collaborator of a content can have multiple use cases, which the proposed implementation should support

  1. Only 1 user can edit content at a time. When a user is editing content, other users get a warning/information that a user is currently editing the content.(lock the content)
  2. Refresh lock when user editing the content until he closes the editor/content
  3. When the creator loses internet connectivity, the lock/unlock mechanism needs to be handled
  4. When the editor unable to get a proper server response, the lock/unlock mechanism needs to be handled
  5. When the creator comes back from inactivity (sleep mode/gets internet connectivity/switched browser tabs), the lock/unlock mechanism needs to be handled
  6. When there's a manual browser refresh, the lock/unlock mechanism needs to be handled
  7. Lock/unlock mechanism need not be applied in the editors read only mode. (When reviewer opens a content)

Solution -1: Using Lock Service to check content collaboration status.

  1. When a creator is trying to edit a content, the content is locked for that particular user id and device id using the GetLock API.
  2. In the configuration, the editor will also get an Expiry time in milliseconds. This Expiry time is basically the time in which the lock will expire.
  3. The editor will then make use of this Expire time to calculate the interval, which is 1/3rd of the Expiry time to call Refresh Lock API.
  4. For example, if the configuration is set the Expiry time to 30 minutes (1800s), the Refresh Lock API will be called every 10mins (600s).
  5. Every time the Refresh Lock API is called, the Expiry time is extended by its 1/3rd value.
  6. If the creator has lost connectivity due to any technical mishap, the system will release the lock for the content once it hits the Expiry time.
  7. If the same creator is trying to gain access to the same content, we have to get the version key to check the conflict in the content.
  8. If there is a conflict in the content, we have to get the latest content and lock the content. 


  1. To track user idle time, we will be using Idle.js (https://github.com/shawnmclean/Idle.js). But there are a few exceptions that we need to handle i.e. Iframe, player preview. 
  2. To track timer locally, we will be using Timer.js (https://github.com/husa/timer.js).

When a content is being created or updated, two scenarios arise. 

Scenario 1: With the Internet

When the content is opened, the GetLock API is called.

  1. If the get lock is successful, the creator will continue editing the content. 
  2. If the get lock failed, i.e if someone else is editing, a warning will be shown with the details of the person who has the lock.

When the content is open and idle for X amount of time (X is the same time as refreshLockTime and can be configured),

Idle time warning will be shown with an option to Resume. 

On Resume:

  1. If the current time is beyond expiry time, then we check for version key change. 
    1. If the version key is the same, we call GetLock API. 
    2. If the version key is different, we give a warning. 
  2. if current time  < expire time we will call refresh lock API and will update the expire time which we will get from API response



Scenario 2: Without the Internet

When we get the internet back we will check difference between current time and expire time

  1. if current time  < expire time we will call refresh lock API and will update the expire time which we will get from API response
  2. if current time  > expire time we will check is versionKey changed. 
    1. if version key not matching we will show warning 
    2. if version key is matching, then we will call get lock API 
    3. If user get lock he will continue editing otherwise we will show warning



Scenario 3: API down(500 Internal Server Error)

In the case of API inaccessibility, this situation can be handled in two ways.

  1. Call the API at the Exponential backoff time. 
  2. Call the API at the regular interval with refreshLockTime.